The invention generally relates to methods of forming vinyl or allyl(thio)carbamates and more particularly to a vinylchloroformate-free method of synthesizing (N-vinyloxycarbonyl)-3-aminopropyltris(trimethylsiloxysilane).
Two of the key monomers used in the production of hydrogel contact lenses are (N-vinyloxycarbonyl)-3-aminopropyltris(trimethylsiloxysilane) (RD325) and vinylcarbamate-capped polydimethylsiloxane (RD352). The current synthesis of RD325 consists of reacting vinylchloroformate (VCF) with aminopropyltris(trimethylsiloxysilane). The current synthesis of RD352 involves a triflic acid catalyzed ring opening polymerization of octamethylcyclotetrasiloxane with a vinyl carbamate butyl-capped tetramethyldisiloxane (V2). V2 is prepared by the reaction of VCF with 1,3-(4-hydroxybutyl)-1,1,3,3-tetramethyldisiloxane. Both syntheses are relatively straightforward and result in a high yield of product. A significant drawback, however, of both reactions is that the monomer VCF is used.
Vinylchloroformate is a monomer used in various applications such as, for example, the making of contact lenses. Currently, it is believed that this compound is only available via a multi-step synthesis typically involving the use of phosgene and organomercury intermediates. These intermediates are undesirable in that they present heightened environmental concerns.
Alternative methods for making vinyl carbamates have been developed. For example, U.S. Pat. No. 6,423,862 discloses a multistep method for making a vinyl carbamate that does not necessitate the use of phosgene and organomercury intermediates. However, additional methods of making vinyl or allyl(thio)carbamates that do not require the use of phosgene and organomercury intermediates and are relatively straightforward are still needed.
The present invention addresses the above shortcomings and provides methods for making vinyl or allyl(thio)carbamates that do not necessitate the use of phosgene and organomercury intermediates. In one aspect, the invention provides a method for making a vinyl or allyl(thio)carbamate siloxy compound represented by the formula (I):(CH2═CH(CH2)b-Y—C(O)N)xR1  (I)wherein x is 0 0r 1, b is 0 or 1, Y is O or S and R1 is an organic siloxy containing radical.
Preferably R1 is a mono-functional organic siloxy containing radical having the formula
or a di-functional organic siloxy containing radical having the formula
wherein R2 is alkyl, alkyl ether or haloalkyl and n is 1-150. It should be recognized that the N-propyltris(trimethylsiloxysilane) radical and the difunctional radical are simply preferred embodiments. For example, when the alkyl portion of this radical is present it may be from 1 to 20 carbons in length and the methyl groups present on the mono- or di-functional siloxy containing radical may be partially or completely substituted with, for example, fluorine atoms or a fluorinated side chain radical. Such variations in the initial reactants are within the purview of one of ordinary skill in the art. Preferably, the compound represented by formula (I) is a trisiloxysilane vinylcarbamate in which instance b is 0, Y is O and R1 is a substituted or unsubstituted trisiloxysilane group. Alternatively, the compound represented by formula (I) is a vinyl or allyl (thio)carbamate-capped polysiloxane.
The method comprises:    (a) reacting a compound represented by formula (II):CH2═CH(CH2)bOSi(CH3)3  (II)wherein b is 0 or 1,with a compound represented by formula (III):(Y═C═N—(CH2)m)x—R1  (III)wherein x is 0 or 1, Y is O or S, m is 0 to 20 and R1 is an organic siloxy containing radical to form the compound of formula (I):(CH2═CH(CH2)bYC(O)N)xR1  (I)wherein x is 0 or 1, b is 0 or 1, Y is O or S and R1 is a mono- or di-functional organic siloxy containing radical.